Reflexiones de un león

Tango Audio Restoration

Tango music was recorded with equipment much inferior to what is available today. Adding to that, the record companies threw away the master’s leaving us with reproductions based on the shellac records that further deteriate the sound.

For many of the commercial releases of tango music, the Reliquias series, the 78RPM series etc, the transfers have been cleaned and the noises removed for the music to become more clear and easy to listen to. And believe me, if you haven’t listened to a shellac record from the 1920s, you probably have no idea how much noise and hiss there can be on those.

The problem is, in some cases the audio engineer cleaning the sound gets too excited about his capabilities and applies too much filtering, effectively throwing out some of the music along with the noises he is trying to remove. Because once the signal (the music) is mixed with the noise, there is no way to reliably separate the two completely again.

The industry state of the art has been the Cedar noise removal systems, which are very expensive, professional equipment. Enter the revolution of digital sound and digital signal processing (DSP). Now the same tasks can be performed with much cheaper equipment, often with better results. Adobe Audition is an example of a product that gives you a lot of possibilities in this area, much cheaper, but still rather pricey for an amateur that wants to clean up some old tango recordings.

You see, the great thing about the CTA series of Mr. Akihito Baba is that they are close to raw transfers from the shellac records.

P & M: You can clean some noises during the process of recording CDs these days.

Baba: Yes , but on the other hand I don’t want to cut the noise when I reproduce SPs. I like to reproduce SPs without cutting down hig waves to reduce the noises. You can use an equaliser to cut the noises down well, but I decided not to do so. There are others who make clean sound reproductions in Japan. But there are good SP´s not containing any so-called noises, so you don’t have to cut any noises. When you cut the noises, quite often it loses the other sounds as well at the same time. That’s a shame as well.

The great thing about that is that you can take the old records of Mr. Baba and apply today’s computer tools that use sophisticated algorithms to clean up the sound, often with very impressive results. I wanted to check the capabilities of the free software tools Audacity and Gnome Wave Cleaner. While researching them, I saw references in various forums to a shareware software called Click Repair. It can be tried for free for 21 days, and the results are quite encouraging, even with the default settings, both for Click Repair, and DeNoise by the same author. That they produce good results with little manual intervention is important, as manual audio restoration is a very time consuming process.

I prefer a little noise to over processed sound, but I also prefer no noise to the noise of the old 78 rpms. In the continuum between these extremes, I think the sweet spot for me is more like 80%-90% clean, limiting the probability of audible distortion to the signal of interest, i.e. the music. And I have hope it can be achieved by batch processing the cta discs and others.

The thing I like almost more than the impressive results, is that the software lends itself to automation. There are some adjustments that would ideally be made for each track, and I will make those for each cd instead, and reprocess single files if they turn out problematic. From my experiments so far, the noise profiles of records seem fairly similar, and the amount of noise more or less the same on records from the same years.

To check that you are not removing any important information, you can easily switch between three listening modes, the input signal (unprocessed music), the output signal (the processed music) and the difference (the noise that is removed). By checking the noise, you can be fairly sure you’re not removing any actual musical content by applying too aggressive processing.

It is possible to get better results by doing it manually, but I have no time for redrawing waveforms manually on hundreds or thousands of tracks. Well, not until when I retire 😉

Here are a few samples:

This first one is a nice orchestra with recordings from the 1940s with clicks and pops that were annoying me. The software doesn’t output the noise, but I made a simulation (taking the difference between the original and the processed) to give you an idea of how it sounds:

All these are (to my knowledge) unavailable in pre cleaned versions, so a little restoration will be worthwhile. The next question is: Can the results be even better than some of the commercially processed releases? We’ll get back to that in an upcoming post.

It is very dangerous to make a lot of conclusions from a graphic display of the waveform in a DAW. Manually getting rid of clicks should be your last option in this day and age when you can spend money on stuff like iZotope RX for example. Algorithmix also.

De-noising is probably the easiest way to screw up a song. It is, unfortunately very hard to do. 🙁 Your Pancho is a good example of how hard it is to clean them without making them sound muffled. The processed version is less lively and much more subdued.

Unfortunately my laptop was stolen so I can’t have a go at these songs. But each track is a track as there are many factors as to why noise profiles won’t be the same. It all boils down to how much time one has and wants to invest on it.

Thanks for bringing the attention to this. I’m surprised so many DJs haven’t cleaned a bit their versions.. but then again, I’m a bit of an audiophile 🙂

@Bruno: I agree, use your ears. The illustration is just that – an illustration (taken from the Pancho track).

The 20s stuff is very hard to fix, yes. You’re right about time spent, and this is a demonstration of what can be achieved with little effort. For click removal I used the default settings, no tweaking at all, and moderate noise removal, well a little more aggressive on the Pancho obviously.

I actually think djs don’t clean their records for good reasons, but I’ll get back to that 🙂

@TP: I like them too, La Bruja is denoised by the noise profile of another song on the same album (track 1). All click removal with default 78rpm settings.

I guess it processes the sound 3-5 times real time for click repair depending on the damage on my three year old laptop, and a bit faster for denoise. In addition you have to convert to wav first and back to whatever format you use afterwards.

Dear Simba,
You have done a good job with that Manuel Buzon track, I’m particularly interested to source some of his music which is delightful, but very scarce. Do you mind telling me where you obtained it? I’m a tango dj in Perth Western Australia, and more fussy than most, about sound quality and music quality generally. I just discovered that BA Tango Club have a Buzon cd listed which I immediately ordered, in blind hope…I have just 6 tracks here.
John
PS from my dj experience I think a minimum of crackle removal is OK, the treble is very directional and not noticed by most of the dancers. It’s more important to boost the upper-bass frequencies, above about 200 Hz, that is the food that the dancers need.

I have an idea about track restoration that I don’t have the skills to try. It’s based on the random nature of pops and crackles. It would use their randomness as their Achilles Heel. The starting point would be to obtain at least two different copies of the same 78 track. They would both be digitised and compared electronically, and anything that did not appear on both, would be discarded from the processed version. What do you think?

Your idea is basically how the existing click removal tools work, the recordings are mono recordings, but if you transfer them with stereo equipment, you read both walls of the groove wall, and use statistical analysis to guess what is signal and what is noise. Doing it with more than one disc would be more complicated, aligning the two tracks with differences in speed and various distortions. I’m not really an expert, I suggest you try hydrogenaudio if you want to discuss with the real experts.

ClickRepair seem to have some other software DeNoise and DeNoiseLF which I’ve been checking out. Its a very time consuming process but I quite like the results. I often leave a little bit of hiss still in my final versions. If its too polished it just doesn’t feel as lively.

Hi, who of you knows to work good the rx izotope decracker? I’m using as plugin and also as stand alone interface, i see that i’m not able to remove all the screws on the voice, sometimes doesn’t work. I would like if there is a certain method to set the process by the skews values and the strenght to use on them.

@Dario: Transferring from shellac to digital is much less straight forward than one would think. Long story short: it is next to impossible to make sure you transfer at the correct speed with the correct eq, and you basically have to use your subjective judgement as to which sounds “better”. To my ears, the CTA transfer of La Bruja sounds more natural than the (much faster) El Bandoneón one, which I guess is the most popular alternative.